The invention relates to the distribution of light generated by one or more LEDs through a rod. More particularly, the invention relates to a white light emitting rod including paint distributed in such a way as to both control the angular distribution of light leaving the rod, and to ensure uniform light distribution along the length of the rod.
Recent side emitting rods, such as in U.S. Pat. No. 4,733,332, issued to Agency of Industrial Science and Technology and Daikin Industries, Ltd. and herein incorporated by reference, have used optical facets or fine powder down one side of the rod. These facets or powders serve to outcouple light from the rod in a direction opposite to the facets, and with a relatively narrow angular distribution. These rods are potentially expensive to make, and do not perform well for white light generated by mixing of multicolored LEDs, for example, red, green, and blue (RGB) LEDs.
A flexible rod material is used as an alternative outcoupling approach. This approach uses a narrow white strip embedded in a plastic material. Although this Lambertian scatter enhances the color of mixing of RGB white light, a uniform white stripe leads to a significant reduction in light intensity from one end of the rod to the other.
It would be desirable to uniformly distribute high quality LED-generated white light along the length of a rod, with a controllable angular distribution of light outside the rod. Additionally, it would be desirable that the efficiency with which light in the rod is coupled into the desired distribution is high (preferably at least 70%). It would also be desirable to produce these rods cost effectively.
According to the invention, a side-emitting illumination device for uniformly distributing light is composed of a light source, a light-transmitting rod which permits total internal reflection, and outcoupling material affixed to an outer surface of the rod. The light source, composed of one or more LEDs, passes light through the rod. As light is reflected off the inner surfaces of the rod, it impinges the outcoupling material which controls the angular distribution of light leaving the rod. This configuration ensures uniform light distribution along the length of the rod.
In various embodiments of the invention, the rod can be a flexible rod or a rigid rod. The rod can be shaped like an ellipse, a square, or have a combination of straight and curved edges in cross-section. The combination of straight and curved edges can vary in configuration along the length of the rod.
In other embodiments, the outcoupling material is white paint or fine white dots with varying packing density, distributed in such a way as to control the angular distribution of light leaving the rod. The white paint or fine white dots are distributed in such a way as to ensure uniform light distribution along the length of the rod.
In another embodiment the side-emitting illumination device includes a mirror at an end of the rod away from the light source to reflect light which reaches the end of the rod, increasing the outcoupling efficiency of the system.
The invention provides several advantages. The side-emitting illumination device allows for high quality white light distribution along the length of a rod, with a controllable angular distribution of light outside the rod. Additionally, the efficiency with which light in the rod is coupled into the desired distribution is high. Further, the heat generated by the light source is separate from the rod, and LED white light generated from red green and blue LEDs allows for changing color temperatures and adding dynamic color effects. Also, the size of the light engine system is smaller than currently required sources. Finally, the side-emitting illumination device can be produced cost effectively.